1. Field of the Invention
The present invention relates to a stereoscopic microscope which comprises an objective lens system, a vari-focal optical system which comprises at least an image surface, and is coaxial with the objective lens component and common to right and left optical paths, and a pair of right and left observation optical systems each of which is disposed after the vari-focal optical system, and comprises an aperture stop, an imaging lens component and an eyepiece the microscope being configured as an eccentric optical system wherein right and left observation optical axes determined by the pair of right and left aperture stops pass through locations different from that of an optical axis of the vari-focal optical system.
2. Description of Related Art
Stereoscopic microscopes which provide magnified stereoscopic information of objects are useful for performing works on objects which are being observed. Since stereoscopic microscopes are effectively used for surgical operations in particular, description will first be provided of a surgical microscope.
In order to enable more delicate surgical operations, it is desired to configure the surgical microscope so as to allow an image to be observed by a plurality of persons at the same time in optional directions. Therefore, there are known surgical microscopes such as a stereoscopic microscope disclosed by Japanese Patent Kokai Publication No. Hei 5-173079 which is configured to pass a light bundle which is to be used for forming images to be observed by right and left eyes through a single vari-focal optical system.
This publication discloses a fact that a rotating direction can be freely changed by rotating, around an optical axis of a vari-focal system, aperture stops for right and left optical paths which are disposed after the vari-focal system.
Further, an optical system disclosed by Japanese Patent Kokai Publication No. Hei 7-140395 is known as another conventional example of stereoscopic microscope of this type. This conventional example corrects aberrations more favorably and configures the optical system more compact by disposing an optical system which relays an image one cycle after the vari-focal optical system of the stereoscopic microscope disclosed by Japanese Patent Kokai Publication No. Hei 5-173079.
The stereoscopic microscope mentioned above as the conventional example uses an optical system designed as an achromat which favorably corrects chromatic aberration of the C-line and F-line. Though colors are not so remarkable in an optical system which is not eccentric even when it is designed as an achromat, an eccentric optical system like this conventional example has a defect that it allows colors to be conspicuous. This is because the eccentricity is equivalent to enlargement of a numerical aperture, whereby colors are shifted laterally due to lateral chromatic aberration in observation optical systems. When images to be observed by a right eye and a left eye are formed by an optical system which has lateral chromatic aberration, outward and inward portions of contours of the images (hereinafter referred to as inwards and outwards respectively) are differently colored. In case of the conventional example described above, for example, inwards of images are yellow, whereas outwards are violet. When such colored images are fused for stereoscopic observation, an inward of an image to be observed by the left eye is overlapped with an outward of an image to be observed by the right eye, whereby an image formed by overlapping the yellow with the violet seems flickering and aggravates fatigue of the eyes. It is not proper to observe such an image through a surgical microscope for surgical operations which can require long periods of time.
For correcting the lateral chromatic aberration which colors the outwards of the images in violet, the ordinary correction of chromatic aberration of the C-line and the F-line is insufficient, and it is necessary to design an optical system as an apochromat which corrects chromatic aberration not only of the C-line and the F-line but also that of the g-line. In other words, it is required to correct secondary spectra.